Recently, ink-jet recording system has been applied in various fields of printing works such as photograph imaging, various types of printings, markings and a specific printing such as a color filter because it enable to form an image easily and with low cost.
Ink-jet ink used for the ink-jet recording includes various types of ink such as an aqueous ink containing water as a principal solvent, an oily ink principally containing a non-volatile solvent at room temperature and substantially containing no water, a non-aqueous ink principally containing a solvent volatile at room temperature and substantially containing no water, a hot-melt ink which is solid at room temperature and thermally melted for printing and an active light curable ink capable of curing by active rays such as light, which are selected in accordance with the use.
Besides, a recording medium made from plastics such as poly(vinyl chloride) and polyethylene is used for prints to be posted outdoors which is required to have a weather resistance for a long period and ability of contacting with a curved surface is used, particularly a medium made from soft poly(vinyl chloride) is used in wide field of use. The ink-jet recording method is applied as a method suitable for making small amount and diverse kinds of printing matters since plate making is not necessary and the time for finishing is short in such system, though many methods are applied for printing an image on the Poly(vinyl chloride).
Hitherto, the non-aqueous ink containing cyclohexanone as the principal solvent is used on the occasion of printing on the soft poly(vinyl chloride) recording medium, for example, an ink-jet ink containing cyclohexanone is disclosed, cf. Patent Document 1). Cyclohexanone has high dissolving ability for soft poly(vinyl chloride) so that the pigment contained in the ink is come into soft poly(vinyl chloride). Therefore, high anti-abrasion ability and high glossiness of the printed matter can be obtained. However, cyclohexanone is regulated as the First Class Organic Solvent under Organic Solvent Intoxication Preventing Rules (based on Japanese Occupational Health and Safety Law), and causes a problem of safety and a local gas exhausting device is necessary on the occasion of handling the ink-jet ink containing cyclohexanone.
In contrast to that, non-aqueous ink containing no cyclohexanone is developed and marketed. For example, non-aqueous inks containing a solvent such as N-methylpyrrolidone and amide as the solvent capable of dissolving poly(vinyl chloride) in place of cyclohexanone causing the above problems are disclosed, cf. Patent Documents 2 and 3. Moreover, a non-aqueous ink containing a fixing resin such as a vinyl chloride-vinyl acetate copolymer and an acryl resin for improving the stoutness of the image such as anti-abrasion ability is disclosed, cf. Patent Documents 4 and 5. An ink-jet ink which is inhibited some degree in the odor thereof and has the abrasion resistivity of image formed thereby on poly(vinyl chloride) medium can be obtained by such constitution. However, a problem is newly found that the irregular action of the ink-jet printing head is caused when such ink-jet ink is used for a prolonged period so that normal image formation cannot be performed gradually. Accordingly, any non-aqueous ink-jet ink is not obtained yet, which has no problem of the safeness and odor and sufficient suitability for printing onto poly(vinyl chloride) and can be used for a long period.
Patent Document 1: Japanese translation of PCT international application 2002-526631
Patent Document 2: Japanese published patent application (JP-A) 2005-15672
Patent Document 3: JP-A 2005-60716
Patent Document 4: JP-A 2005-36199
Patent Document 5: WO 2004/007626